Six minutes later, Paddock began firing on the crowd of concertgoers below, police said.
The security guard, Jesus Campos, was struck in the leg as the gunman, from behind his door, shot into the hallway on the 32nd floor.
Although Campos alerted hotel security, Lombardo said police were not aware of the incident until they stormed Paddock's room ten minutes later.
Campos was shot while investigating an alarm that was unrelated to Paddock's room.
But officials said Monday that Paddock shot Campos before his mass shooting, and they now don't know why Paddock stopped his attack on the crowd.
But on Monday, the timeline changed.
At a news briefing on Monday, Las Vegas sheriff Joseph Lombardo revealed an update in the timeline of the shooting that occurred at the Route 91 Harvest festival last Sunday. Paddock, who had rigged a camera to see anyone approaching, shot the guard through the door.
"In coordination with the FBI's behavioral analysis unit, a comprehensive picture is being drawn as to the suspect's mental state and now we do not believe there is one particular event in the suspect's life for us to key on", Lombardo said.
"It doesn't say much for hotel security", Heal said.
Representatives for the Mandalay Bay hotel casino and the union representing Mandalay Bay's security guards did not immediately respond to messages seeking comment.
Police are now looking to speak to any escorts who Paddock may have been with in the days before the massacre took place. Investigators believe Paddock was planning to escape after the massacre.
The story was originally published at 3:25 p.m.